TW202113320A - Tightness test of a liquid-filled test specimen - Google Patents

Abstract

A method for tightness test of a test specimen (14) filled with a liquid (12) and having an internal pressure which is lower than atmospheric pressure, comprising the following steps: placing the test specimen (14) into a test chamber (16); evacuating the test chamber (16) to a pressure which is lower than the internal pressure inside the test specimen (14); withdrawing residual gas constituents from the test chamber together with gas constituents desorbing from a wall of the test chamber and parts of the liquid escaping through a leak in the test specimen from the latter, without any carrier gas being supplied to the test chamber from the outside; transporting the extracted residual gas constituents together with the parts of the liquid escaped from the test specimen to a detector (28); and detecting parts of the liquid (12) escaped through a leak in the test specimen (14) by means of a detector (28).

Description

Leak test method for filled liquid samples

The present invention relates to a method for leak detection of a test sample filled with liquid.

Various methods for industrial leak testing are known, in which a test sample filled with a test gas is subjected to negative pressure in a test chamber by evacuating the test chamber. Due to the resulting pressure difference, the test gas escapes into the test chamber through a leak that may be present in the test sample, and the test gas is supplied from the test chamber to the sensor to detect the test gas. For example, in order to conduct a leak test, the food package is actively filled with a test gas such as helium, and then placed in the test chamber. Alternatively, a method of using the gas already contained in the test sample as the test gas when the test sample is placed in the test chamber is known. In this case, there is no need to actively fill the test sample with test gas.

Such methods are described, for example, in DE 10 2014 224 799 A1. When the test sample is placed in the membrane chamber, the gas already contained in the test sample may be an air component such as nitrogen, oxygen, or carbon dioxide. In addition, a gas containing product flavoring substances contained in the test sample or a gas composed of such substances can be used as the test gas. In the case of coffee, the product flavoring substances are, for example, coffee flavoring substances. Another possibility is to use the gas generated by the product contained in the test sample such as food as the test gas. In the case of coffee, this gas may be CO ₂ generated in the coffee bag after a few hours.

In contrast, the present invention relates to leak detection of a filled liquid test sample that does not contain any gas to be used as a test gas and should not or cannot be actively filled with a separate test gas. For example, the situation is as follows: a battery filled with an electrolyte liquid, such as a lithium ion battery filled with dimethyl carbonate as an electrolyte.

In the method described above based on the gas detection principle that flows from the inside of the test sample to the outside, the escaping gas is frequently detected by the gas detector. Test the leak tightness of the test sample by means of the vacuum method. In order to perform a leak test, the test sample is placed in a vacuum chamber. With the aid of a vacuum system, the gas that escapes into the vacuum chamber through the leak in the test sample is continuously exhausted from the vacuum chamber. With suitable sensors in the vacuum system, the leaking gas can be selectively detected. At a sufficiently low pressure, the leaking gas moves toward the sensor sufficiently quickly and freely by diffusion or in the form of molecules.

As an alternative to the method described above based on the gas detection principle that flows from the inside of the test sample to the outside, a technical solution is known that supplies the escaped gas into the gas detector by means of a carrier gas. When the operating pressure in the vacuum chamber is much higher than 1 mbar, the carrier gas method is particularly applied. In these cases, the diffusion rate of the leaking gas to be detected in the vacuum chamber is too slow. This type of carrier gas method is described, for example, in WO 2005/054806 A1, in which a carrier gas stream flows through a test chamber containing a test sample. Purge the test chamber with carrier gas. The test gas escaping from the test sample is transported out of the test chamber together with the carrier gas flow and supplied to the test gas sensor.

In the refrigeration and heating, ventilation and air conditioning industries, it is a well-known technique to check the leakage tightness of test samples filled with liquid coolants (such as heat exchangers). The special feature of these test samples is that the pressurized test sample contains liquid coolant to obtain the coolant liquid phase. In order to perform a leak test on the test samples filled with liquid coolant, the sniffer probe is made to pass through the test sample area to be tested for leak tightness. The sniffer probe absorbs the leak The part escapes into the external atmosphere and vaporizes the coolant and supplies it to the gas detector. The sniffer probe absorbs air from the environment of the test sample and therefore absorbs the leaking gas that is escaping. The leaking gas system is selectively sensed by the corresponding sensor and is therefore distinguished from the absorbed air group Minute.

When a liquid-filled test sample has an internal pressure lower than the atmospheric pressure of the external environment (for example, the internal pressure is in the range of about 50-500 mbar), the sniffer probe type leak detection method cannot be used , This is because if there is a leak, no leaking gas escapes to the outside. For example, in a battery filled with a liquid electrolyte with a low vapor pressure and a negative pressure prevailing therein, any leakage will cause air to enter the inside of the test sample from the external environment of the test sample. It is not possible to detect leaks with sniffer probes.

The leak detection method described above using the test gas contained in the test sample is also not applicable or at least inaccurate. This is because the liquid in the test sample travels to the leaking part when the external environment of the test sample is evacuated Openings or channels and obstruct the outward flow of the test gas or at least substantially affect the escape of the test gas. Therefore, a certain amount of the detected test gas outside the test sample is not a feature of the existence or size of the leak in the test sample.

EP 1 522 838 B1 describes a method in which a test sample filled with electrolyte is contained in a test chamber whose internal pressure is lower than the pressure inside the test sample. According to the carrier gas method, purified air or ambient air serving as a carrier gas is supplied to the test chamber to supply the liquid component escaping from the test sample into the detector.

In view of this situation, one of the objectives of the present invention is to provide a leak detection method for test samples filled with liquid whose internal pressure is lower than or equal to atmospheric pressure.

The method of the present invention is defined by the characteristics described in claim 1.

According to the present invention, the test sample filled with liquid is placed in the test chamber. The liquid is contained inside the test sample. The internal pressure inside the test sample is lower than or equal to atmospheric pressure. After the test sample has been placed in the test chamber, the test chamber is evacuated to a pressure lower than the internal pressure inside the test sample and lower than atmospheric pressure. The residual gas components contained in the test chamber are drawn out together with the gas components desorbed from at least one test chamber wall and any part of the liquid that travels from the test sample to the test chamber through the leakage part. Carrier gas is supplied in the test chamber. The detector selectively detects the part or particles of the liquid escaping from the test sample.

It is particularly important for the present invention that no external carrier gas is supplied to the test chamber. The carrier gas should be sourced from a carrier gas source connected to the test chamber or absorbed from the environment. In particular, there is no air flow along the surface of the test sample. On the contrary, the part or particles of the liquid escaping from the test sample are extracted from the test chamber together with residual gas components and supplied to the detector. No carrier gas is required.

The part of the liquid that escapes through the leakage part may be molecular particles in a vaporized state. Vaporization can occur when the liquid escapes from the test sample. Typically, the liquid vaporizes at the exit of the leak channel, which extends through the loose wall of the test sample. The vapor pressure of the liquid at room temperature (approximately 15°C to 25°C) can be lower than 500 mbar. In particular, the test sample may be a battery such as a lithium ion battery, and the liquid may be an electrolyte such as dimethyl carbonate.

The laboratory can be configured as a hard laboratory with hard walls. Alternatively, the test chamber can be configured as a membrane chamber, which is characterized in that it contains at least one flexible wall area that is pumped towards the test sample during evacuation, thereby reducing the membrane Chamber volume. In addition, a membrane chamber having a wall entirely composed of a flexible membrane provides the advantage that the wall attached to the test sample supports the test sample, which is particularly advantageous in the case of the flexible test sample.

The detector includes a sensor that selectively detects the part or particles to be detected in the liquid and can thus distinguish it from other parts or gases. The part of the escaped liquid can be liquid and supplied to the detector. The detector must be able to analyze the liquid and selectively detect the liquid contained in the test sample. The escaped liquid can be supplied to the detector in the form of mist or aerosol.

Alternatively, it may be provided that the liquid vaporizes when it escapes through the leak in the test sample, and the escaped portion of the liquid is supplied to the detector in a vaporized state, that is, in a gas phase. The detector must be configured as a gas detector and must be able to analyze the gas and distinguish the liquid in the test sample in its gas phase form from other gases. Here, it is crucial that the liquid contained in the test sample changes its gas phase from the liquid phase only when it leaves the test sample, that is, outside the test sample or in the opening or passage of the leak. Therefore, the gas in the test sample is not used as the test gas because the liquid in the test sample is liquid, even when the liquid escapes through the leak and vaporizes.

The detector used for the part of the liquid to be detected can be gas detection such as gas spectrometer, gas chromatograph, infrared radiation absorption detector or detector with chemical sensor or semiconductor sensor Device.

No carrier gas is introduced into the test chamber. In detail, as in the conventional carrier gas method applied to gas leakage detection, a constant flow of carrier gas is not supplied to the test chamber. On the contrary, the residual components inside the test chamber and the gas components desorbed from the walls of the test chamber are used to transport the part or particles of the liquid that escapes into the test chamber through the leak in the test sample to the detector. Therefore, a mixture of gas components from the inside of the test chamber or from the walls of the test chamber and the part of the liquid contained in the test sample and particles are supplied to the detector and rely on the detection for detecting the part transported by the gas Analysis.

Preferably, the gas used to transport the liquid is supplied to the detector only when the pressure limit value is reached in the test chamber or the connecting line between the test chamber and the vacuum pump that evacuates the test chamber. This pressure limit can range between 2 mbar and 50 mbar and it is preferably lower than 20 mbar. The vacuum pump, which is preferably a membrane pump, can be connected to the test chamber via a valve and/or a gas line connecting the vacuum pump and the test chamber. At the beginning of the evacuation, close the valve. When the pressure limit is reached, the valve is opened and part of the gas flows into the detector, while the remaining main gas flow continues to be extracted by the membrane pump. Here, especially in the case of a vacuum pump configured as a membrane pump, in contrast with the conventional carrier gas method, the accumulation of liquid escaping from the leak is realized. When the pressure limit is reached, the liquid part that has accumulated so far is supplied to the detector.

Preferably, it is provided that the test sample is purged with a purge gas in the test chamber to remove the part of the liquid adhering to the test sample. Preferably, the test sample is purged with purge gas before actual leakage detection, for example, before evacuating the test chamber.

It is conceivable that the accumulation of the part of the liquid escaping from the leak occurs during a period of time before the part of the liquid or the mixture of the part of the residual gas and the liquid is supplied to the detector for analysis purposes. In the test room or in the connecting pipeline.

It can be calibrated by means of a test leak filled with test liquid. The test leak can be configured as a capillary leak, in which the test liquid escapes through a capillary with a known size formed in the wall of the test leak. Alternatively, the test leak may be a permeable liquid leak, wherein the area of the test leak wall is configured as a membrane with known permeation characteristics for the test liquid. With this type of calibration, the correlation between the amount of the detected part of the liquid and the size of the leak can be obtained and recorded during the actual leak detection, so as not only to determine the existence of the leak, but also to determine its size.

According to the present invention, it can be specifically provided that the size of the leakage portion is obtained based on the detection of the portion of the liquid escaping from the leakage portion.

In both embodiments, the test sample 14 filled with the liquid 12 is contained in the test chamber 16. In the embodiment of the present invention, the test sample 14 is a battery filled with liquid electrolyte. In the embodiment of the present invention, the test chamber 16 is a conventional hard test chamber.

The test chamber 16 is provided with a vacuum connector 22 for connecting it with a vacuum pump 24, and the test chamber 16 can be evacuated by means of the vacuum pump 24. For this purpose, the vacuum pump 24 includes at least one vacuum pump configured as a membrane pump. The test chamber 16 and the vacuum pump 24 are connected to each other by a connecting line 26 in a gas conduction manner so that the vacuum pump 24 can extract gas from the test chamber 16 through the connecting line 26.

The connection line 26 connecting the vacuum pump 24 and the test chamber 16 is connected to the detector 28 to analyze and detect the portion of the liquid 12. In the two embodiments of the present invention, the detector 28 is a selective gas detector configured as a mass spectrometer. For example, the sensor of the selective gas detector selectively detects the liquid 12 The molecular part and can distinguish the molecular part from other gases. The detector 28 is a part of a mass spectrometer vacuum system 20 including a front vacuum pump 19 and a high vacuum pump 18 for evacuating the mass spectrometer.

The detector 28 is connected to the connecting line 26 via the gas conduction detection line 21 in a gas conduction manner. The detection pipeline 21 is provided with a throttle valve 38 for adjusting the air flow that diverges from the connecting pipeline 26 and a valve V2 for selectively closing the detection pipeline 21. In order to measure the pressure inside the connecting pipeline 26, the connecting pipeline 26 is connected to the pressure sensor 17 in a gas conduction manner.

Part of the liquid 12 escapes through the leak in the test sample 14 and travels to the test chamber 16. When the liquid 12 escapes from the test sample 14, it can be vaporized so that the escaped portion of the liquid 12 can be in its gaseous state.

The detector 28 operates as a mass spectrometer in a vacuum system at a pressure lower than the pressure inside the test chamber 16 and lower than the pressure at the connection point 40 between the connection line 26 and the detection line 21. In the membrane pump 24 for evacuating the test chamber 16 of the present invention, a high vacuum is not generated in the test chamber 16. Conversely, the membrane pump 24 generates a pressure in the range of several millibars. The membrane pump 24 extracts residual gas components from the test chamber 16. In addition, when the pressure in the test chamber 16 reaches a pressure in the range of about 10 mbar, the gas components are desorbed from the walls of the test chamber, and these gas components are also extracted by the membrane pump 24. These gas components, that is, the residual gas components from the test chamber 16 and the gas components desorbed from its walls are absorbed from the test sample 14 to the part of the liquid 12 in the test chamber 16 through the leak. These parts of the liquid 12 are supplied to the detector 28.

After evacuation, the vacuum pressure inside the test chamber 16 is several millibars. The diffusion of the part of the liquid 12 that has escaped from the test sample 14 and vaporized is still inert under this pressure. Without using any carrier gas and supplying any carrier gas from the outside into the gas chamber 16, the gas component is used to accelerate the transportation of the escaped part of the liquid 12 to the detector 28.

Alternatively, it is conceivable that the accumulation of the liquid portion escaping from the test sample 14 occurs inside the test chamber 16 or the connecting line 26 before the portion of the escaping liquid 12 is supplied to the detector 28. For this purpose, it is conceivable that a valve not shown in Fig. 1 is provided between the connection point 40 and the membrane pump 24. When the inside of the test chamber 16 reaches a sufficient vacuum pressure, the valve is closed to cause the escaped liquid Part of it accumulates inside the test chamber 16 or in the connecting pipeline 26 between the test chamber 16 and a valve not shown, and then is detected. For detection purposes, valve V2 can be opened. During the accumulation phase, valve V2 can be closed or opened.

The second embodiment depicted in FIG. 2 is different from the first embodiment in FIG. 1 in that the section 30 of the detection line 21 including the valve V2 is bridged by the section 36 including the other valve V3 so that The valves V2 and V3 are connected in parallel. In the section 32 of the connecting pipeline 26, a valve V1 is provided between the connecting point 40 including the connecting pipeline 26 of the section 30 and the connecting point 42 between the connecting pipeline 26 and the section 36. To evacuate the test chamber 16, the valve V1 is opened. Close valve V2. The same applies to valve V3. When the valves V2 and V3 are closed and the valve V1 is opened, the vacuum pump 24 only evacuates the test chamber 16. The detector 28 of the second embodiment is also a mass spectrometer including an independent vacuum system. The inlet area into the mass spectrometer is also evacuated via the vacuum pump 24. For this purpose, valve V2 is kept closed, while valve V1 is closed and valve V3 is opened to evacuate the inlet area into the mass spectrometer to the required vacuum pressure. After evacuating, the valve V1 is closed and the valves V2 and V3 are opened to perform a measurement operation, so that the measurement medium is transported from the test chamber 16 through the detector 28 via the vacuum pump 24.

In the case where there is a leak in the test sample 14, the part of the liquid 12 contained in the test sample 14 travels into the test chamber 16. The liquid can be dimethyl carbonate used as an electrolyte in lithium ion batteries. In the lithium ion battery, after the test chamber 16 is evacuated, there is generally a vacuum pressure higher than the pressure inside the test chamber 16 in the area outside the test sample 14. The liquid electrolyte vaporizes when it escapes from the test sample 14 through the leakage part, so that the to-be-detected portion of the liquid 12 can exist in the form of molecular particles in the gas phase.

The portion of the liquid 12 is transported through the test chamber 16 via the lines 26, 30, 21 and to the detector 28 and further to the pump 24 via the line 36. A mixture of gas components originating from the inside of the test chamber 16 and/or from the walls of the test chamber 16 and the transported part of the liquid 12 is generated. The selective sensor of the mass detector 28 detects the part of the liquid 12 and can distinguish it from the gas composition of the test chamber 16. The detection of the portion of the liquid 12 escaping through the leak of the test sample 14 serves as an indication of the presence of the leak in the test sample. The amount of the detected portion of the liquid 12 can indicate the size of the leak.

In addition, the portion of the liquid 12 that escapes through the leak in the test sample 14 can accumulate in the test chamber 16 before detection occurs. For this purpose, the valves V1, V3 are closed during the accumulation phase. In addition, valve V2 can also be closed during the accumulation phase. When a predefined period of time has elapsed, the valve V2 is opened so that the accumulated part of the liquid 12 is supplied to the detector 28.

After the accumulation phase, the accumulated gas can be further transported to the detector 28 via the gas composition from the test chamber 16. For this purpose, no carrier gas from the outside is supplied into the evacuated test chamber 16. In the case that the test chamber 16 is closed, it is necessary to wait until a portion of the liquid 12 accumulates in the test chamber 16 within a predefined period of time. The detector 28 is set to a pressure lower than the pressure prevailing in the test chamber 16 by virtue of the vacuum pumps 18 and 19. When the valve V2 is opened, the accumulated part of the liquid 12 is transported to the detector 28 and detected there.

Select the guide value of the throttle valve 38 and the threshold value of the pressure in front of the throttle valve 38 (on the left in the figure) where the valve V2 is opened, so that it enters the chamber volume of the mass spectrometer 28 through the throttle valve 38 The air inlet causes a pressure increase of ^{not more than 10 -4 mbar.} Preferably, the pressure threshold under laboratory conditions is about 5 mbar.

With the aid of the mass spectrometer 28, a signal is generated based on the measured mass, which is characteristic of the characteristic component (electrolyte component) of the liquid 12. The measurement signal is compared with the threshold value, where exceeding the threshold value is regarded as an indication of the leakage in the test sample 14. After the measurement, the valve V2 is closed to ventilate the test chamber and the test sample 14 can be removed from the test chamber 16.

The method of the present invention does not require any advanced vacuum pump, such as a high vacuum pump, for evacuating the test chamber 16, but only a simple vacuum pump that can reach a final pressure of less than 10 mbar, such as a membrane pump.

The basic difference between the two embodiments of the present invention is that in the embodiment of FIG. 2, after the valve V1 has been closed and the valves V2 and V3 have been opened, when the defined pressure threshold has not been reached, the travel ratio must be In the embodiment of FIG. 1, the distance from the throttle valve 38 to the mass spectrometer 28 is shorter. In the area between the throttle valve 38 and the mass spectrometer 28, the pressure inside the detection pipeline 21 is low, that is, less than 10 ^-4 mbar, so that the gas can move freely in molecular form in this area. Therefore, the time required for the gas to diffuse to the mass spectrometer 28 can be ignored.

For example, on the side facing away from the throttle valve 38 of the mass spectrometer, that is, on the left-hand side of the throttle valve 38 in the diagram, the pressure inside the pipelines 26, 30, 32, and 36 is 5 mbar. Viscous flow conditions are ubiquitous, so the measurement gas must be diffused through the residual gas along this distance, thereby causing a time delay. In FIG. 1, the diffusion distance from the connecting point 40 between the connecting line 26 and the vacuum line 21 to the throttle valve 38 is longer than the distance between the connecting point 44 of the lines 30, 36, and 21 and the throttle valve 38 in FIG. Diffusion distance.

12: Liquid 14: Test sample 16: Laboratory 17: Pressure sensor 18: High vacuum pump 19: Front vacuum pump 20: Mass spectrometry vacuum system 21: Detection pipeline 22: Vacuum connector 24: Vacuum pump 26: Connect the pipeline 28: Detector 30: Detect pipeline section 32: Connecting pipeline section 36: Pipeline section 38: Throttle valve 40: connection point 42: connection point 44: connection point V1: Valve V2: Valve V3: Valve

Hereinafter, two embodiments of the present invention will be explained in detail with reference to the drawings, in which: Figure 1 shows a block diagram of the first embodiment; Fig. 2 shows a block diagram of the second embodiment.

12: Liquid

14: Test sample

16: Laboratory

17: Pressure sensor

18: High vacuum pump

19: Front vacuum pump

20: Mass spectrometry vacuum system

21: Detection pipeline

22: Vacuum connector

24: Vacuum pump\membrane pump

26: Connect the pipeline

28: Detector\Mass Spectrometer\Mass Spectrometer Detector

38: Throttle valve

40: connection point

V2: Valve

Claims (15)

A method for leak testing of a test sample (14) filled with a liquid (12) and having an internal pressure lower than atmospheric pressure, which includes the following steps: Place the test sample (14) in the test room (16); Evacuate the test chamber (16) to a pressure lower than the internal pressure inside the test sample (14); The residual gas components are extracted from the test chamber together with the gas components desorbed from the walls of the test chamber and the part of the liquid escaping from the test sample through the leakage part in the test sample, which does not enter the test chamber Supply any carrier gas from outside; The extracted residual gas components are transported to the detector (28) together with the parts of the liquid escaping from the test sample; and The part of the liquid (12) that escapes through the leak in the test sample (14) is detected by means of a detector (28). The method according to claim 1, wherein the transported part of the liquid (12) is a molecular part in a vaporized state. The method according to claim 1 or 2, wherein the vapor pressure of the liquid (12) at room temperature is lower than 500 mbar. The method according to any one of the preceding claims, wherein the test sample (14) is a battery and the liquid is an electrolyte. The method according to any one of the preceding claims, wherein the test chamber (16) is a rigid test chamber or a membrane chamber. The method according to any one of the preceding claims, wherein the detector (28) comprises a sensor that is selective for the liquid portion to be detected. The method according to claim 6, wherein the detector (28) is a gas detector such as a mass spectrometer, a gas chromatograph, an infrared absorption detector or a detector with a chemical or semiconductor sensor . The method according to any one of the preceding claims, wherein the detector (28) is operated in a vacuum system at a pressure lower than the pressure inside the test chamber (16). The method according to any one of the preceding claims, wherein the gas components and the liquid to be detected are supplied to the detector (28) only when a predefined pressure limit value has been reached in the laboratory section. The method according to claim 9, wherein the pressure limit value is in the range of 2-100 mbar and preferably lower than 10 mbar. The method of claim 9 or 10, wherein the detector is connected to the test chamber (16) via a valve (V2), the valve (V2) is closed at the beginning of the evacuation of the test chamber and only when the pressure has been reached Open at limit value. The method according to any one of the preceding claims, wherein the test sample (14) is purged by a purge gas after being placed in the test chamber (16). The method according to any one of the preceding claims, wherein the accumulation of the parts of the liquid (12) escaping from the test sample (14) is detected by the detector (28) Part of it occurred in the test chamber (16) or in the connecting pipeline during a period of time before. The method according to any one of the preceding claims, wherein before placing the test sample (14) in the test chamber (16), a test leak containing a test liquid is used, and the test leak The leak is placed in the test chamber, the test chamber is evacuated and the detector (28) is used to detect the part of the liquid escaping from the leak to calibrate the detector. The method according to any one of the preceding claims, wherein the gas contained in the test sample (14) when the test sample (14) is placed in the test chamber (16) is not used as a leak detection Test gas.

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